Method of manufacturing sodiumvapour discharge tubes



United States Patent M 3,023,069 METHOD OF MANUFACTURING SODIUM- VAPOUR DISCHARGE TUBES Martinus Henricus Adrianus van de Weijer, Eindhoven,

Netherlands, assignor to North American Philips Company, Inc., New York, N.Y., a corporation of Delaware No Drawing. Filed Dec. 14, 1959, Ser. No. 859,093 Claims priority, application Netherlands Dec. 9, 1958 2 Claims. (Cl. 316-26) The present invention relates to methods of making sodium-vapour discharge tubes having a neon gas-filling to which argon is added.

The usual addition of approximately 0.1 to 1% of argon serves to reduce the ignition voltage of the tube. During operation of the tube, sodium ions and also noble gas ions are produced, in particular ions of the added argon, the ionization potential of which is lower than that of neon. These ions are urged towards the wall where they are neutralised' by recombination with electrons. Not all of these ions return as free gas atoms; some of them adheres to the wall so that the concentration of the argon addition decreases. If this proceeds to an undue degree the ignition voltage is insuificiently reduced, the tube ig-' nites no longer and the end of its lite-time is reached.

The present invention has for its object to improve upon this.

In accordance with the invention, the tube is first filled with argon in which an argon discharge is produced, subsequently to which the definite metaland gasfilling is provided.

By this argon discharge the glass wall of the discharge vessel is, as it were, previously charged with argon.

In a discharge tube having a diameter of 8 to mms, the argon discharge is preferably maintained 10 to minutes at a current stren th of 0.5 to 1.5 amps, in argon of 0.10 to 0.15 mercury pressure.

In order that the invention may be readily carried into efiect, an example will now be described in detail.

A U-shaped sodium vapour discharge tube is housed in an evacuated cylindrical bulb. The discharge tube consists of lime glass and has an outside diameter of 12 mms. It is internally provided with a layer of a sodium-resistant glass, the composition of which may be as follows: 10

to 30% by weight of B 0 0 to 15%, by weight of K 0,

20 to by weight of CaO-l-BaO and 10 to 40% by Patented Feb. 27, 1962 weight of A1 0 In the present case the sodium-resistant glass has the following composition:

24% by weight of B 0 6% by weight of K 0 10% by weight of CaO 38% by weight of BaO 22% by weight of A1 0 The tube comprises activated thermionic electrodes at its ends and has a length of cms. between the electrodes, measured along the axis of the tube. The tube contains approximately 1000 mg. of sodium metal and has a neon gas-filling of approximately 13 mins. mercury pressure at room temperature, to which approximately 0.5 vol. percent of argon is added. During normal operation with a tube current of 0.9 amps. the tube dissipates approximately w. and has an ignition voltage of 390 v. at the beginning of its lifetime. It is supplied from a source of alternating voltage of 470 v. open circuit voltage. This tube has a lifetime of approximately 2500 operation hours, whereafter it fails to ignite upon connection to said supply source.

If, however, the same tube is first filled only with argon of approximately 0.1 mm. mercury pressure and a discharge is maintained in this medium for approximately 15 minutes at a current strength of approximately 1 amp, its lifetime is found to reach 5000 operation hours.

What is claimed is:

1. A method of manufacturing a sodium vapor electric discharge tube having a neon gas-filling comprising the steps, filling the tube with argon, producing an electrical discharge in the argon, removing the argon, and thereafter filling the tube with sodium and neon containing about 0.5% by volume of argon.

2. A method of manufacturing a sodium vapor electric discharge tube having a neon gas-filling as claimed in claim 1 in which the argon filling is at a pressure of 0.1 to 0.15 mm. Hg, and the electrical discharge is maintained for about 10 to 20 minutes at a current strength of about 0.5 to 1.5 A.

Gross Mar. 24, 1931 V 

1. A METHOD OF MANUFACTURING A SODIUM VAPOR ELECTRIC DISCHARGE TUBE HAVING A NEON GAS-FILLING COMPRISING THE STEPS, FILLING THE TUBE WITH ARGON, PRODUCING AN ELECTRICAL DISCHARGE IN THE ARGON, REMOVING THE ARGON, AND THEREAFTER FILLING THE TUBE WITH SODIUM AND NEON CONTAINING ABOUT 0.5% BY VOLUME OF ARGON. 